Method of countergravity casting

Abstract

In the mold-immersion type countergravity casting method, a resin-bonded particulate mold is formed in-situ in the vacuum chamber used to draw melt into the mold by: providing the chamber with a porous wall; positioning a gasifiable pattern in the chamber; embedding the pattern in a mass of mold-forming particulate containing a chemically curable precursor of the resin binder; and passing a curing gas through the porous wall and mass to cure the resin and unify the mass about the pattern. Thereafter, the mold is immersed in an underlying pool of molten metal and a vacuum drawn in the chamber to displace the pattern in the mold with metal.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In the process for the vacuum countergravity casting of metal comprising the principal steps of positioning a porous, resin-bonded particulate mold in the mouth of a container defining a vacuum chamber, said mold defining a cavity for receiving and shaping molten metal therein and having at least one gate in the underside thereof for admitting said metal into said cavity, immersing said underside and gate(s) into an underlying pool of molten metal, drawing a vacuum in said chamber sufficient to draw said molten from said pool into said cavity, removing the metal-filled mold from said pool, and discharging said mold from said chamber after the metal therein has substantially solidified, the improvement comprising: providing said container with a porous, gas-permeable wall spaced from said mouth and separating said chamber from a gas plenum on the backside of said wall;   orienting said container with its mouth facing upwardly;   positioning a gasifiable pattern in said chamber for shaping said cavity;   embedding said pattern in a mass of mold-forming particulate containing a chemically curable precursor or said resin, said mass at least in part protruding beyond said mouth to provide an immersible mold portion upon curing;   passing sufficient curing gas through said wall and mass to form said bonding resin from said curable precursor and to bond said particulate together in said chamber and portion;   orienting said container such that said immersible portion underlies said chamber; immersing said portion in said pool; and   applying said vacuum in said plenum to (1) draw said metal into said cavity and therewith gasify and displace said pattern therein, and (2) remove the pattern gasification products from said cavity through said porous mold.   
     
     
       2. The process according to claim 1 wherein said particulate comprises foundry sand. 
     
     
       3. The process according to claim 2 wherein said curing gas catalyses the curing of said precursor. 
     
     
       4. The process according to claim 2 wherein said gas reacts with said precursor. 
     
     
       5. The process according to claim 1 including the step of applying superatmospheric pressure behind said wall to effect said discharging.